Refactored the YamlFileLoader to remove duplication

The YamlFileLoader now uses the ArrayLoader by composition rather than
inheritance, allowing to extend from the AbstractFileLoader, which is way
more logical.
Changed the parsing of Yaml to pas the file content for forward compat

Passing a filename as input to Yaml::parse is deprecated.
Merge pull request #70 from stof/refactor_yaml_loader

Refactored the YamlFileLoader to remove duplication